Chitosan-graft-benzo-15-crown-5-ether/PVA Blend Membrane with Sponge-Like Pores for Lithium Isotope Adsorptive Separation

Crown ether exhibits a high separation coefficient for lithium isotope separation owing to its precise size selectivity to cations. A crown ether-based solid-liquid extraction method for the lithium isotope separation with a high extraction efficiency is regarded as a valid alternative to the classic liquid-liquid method. A chitosan-graft-benzo-15-crown-5-ether (CTS-g-B15C5)/polyvinyl alcohol (PVA) porous blend membrane for lithium isotope adsorptive separation was fabricated by immersion-precipitation-phase inversion. Results indicated that the finger-like structure of the blend membrane was replaced gradually by a sponge-like structure with the increase of the CTS-g-B15C5 concentration from 20 to 50 wt %. Meanwhile, the porosity and mechanical strength of the blend membrane slightly decreased from 76.9% and 2.68 MPa to 72.5% and 2.02 MPa, respectively, whereas the average pore size increased from 0.33 to 0.73 μm. The obtained CTS-g-B15C5/PVA (50/50 wt/wt) blend membrane exhibited a sponge-like asymmetrical gradient structure and good mechanical strength and used for the solid-liquid extraction experiment. It is found that the distribution coefficient increased from 13.50 to 49.33, and the single-stage separation factor increased from 1.008 to 1.046 with the immobilization amount of crown ether from 1.07 to 2.60 mmol·g-1. It also meets the acceptable separation factor of 1.03 in a large scale of lithium isotope separation. In addition, 6Li and 7Li were enriched in the solid or membrane phase and the aqueous phase, respectively. In summary, the blend membrane has great potential applications in the development of green and highly efficient membrane chromatography for lithium isotope separation.